In order to dispense a stable flow of photoresist in semiconductor processing, gas powered pumps are used for dispensing photoresist. Gas powered pumps can provide a constant dispensing pressure, avoiding small variations that occur with an impeller powered pump. The resist dispensing pump uses a plurality of electronically controlled valves to control the pressure before and after pumping to stabilize the dispenser action.
One example of a resist dispensing pump is the Advanced Compact Resist Dispense (ACRD) system sold by Tokyo Electron Kyushu, Ltd., of Koshi, Kumamoto, Japan. The ACRD system operates on a four step cycle. Prior to dispensing, the photoresist in the pump is pre-pressurized. During the dispense step, the pressurized photoresist is dispensed. Following dispensing, a system time delay is incurred. Lastly, after the pump has completed dispensing the pump is refilled with photoresist.
Although the ACRD pump has improved dispensing pressure stability relative to an impeller powered pump, it is still subject to bubble formation.